LDPC (Low Density Parity Check) codes are a class of Forward Error Correction (FEC) block codes, often used in transmission environments to protect audio and/or video data. These Forward Error Correction codes increase the possibility of receivers recovering from and correcting errors in a received multimedia stream, without the need to retransmit data that is received with errors. The FEC error control system requires the transmitter add redundant data to a data stream. The maximum fraction of errors that can be corrected by the FEC is determined by the way the error correction code is calculated. Examples of FEC are block codes, such as LDPC codes that work on fixed-sized blocks, packets, or symbols of a predetermined size, and convolutional codes that work on bit or symbol streams of arbitrary length. Many types of block error correction codes exist, such as Reed-Solomon or, as already mentioned, the LDPC (Low-Density Parity Check). Other types of error correction codes have been developed for specific use in transmission of digital video streams over IP networks, such as SMPTE 2022 (Society of Motion Picture and Television Engineers), which unlike other typical FEC schemes such as Reed-Solomon, relies on very simple algorithms, and is useful in environments where limited resources are available, such as a Set Top Box receiver for Digital Television.
The DVB-S2 LDPC codes family, which were originally designed for forward error control in satellite communications, have also been used by DVB-T2 (Second Generation Digital Video Broadcasting (DVBI Standard for Terrestrial Channels), and are strongly recommended for DVB-C2 (Second Generation DVB Standard for Cable Channels). OFDM modulation will be adopted as well as the coding technique (BCH+LDPC) specified in DVB-T2 Standard. However, DVB-T2 Standard is designed for use in the terrestrial wireless channel while the DVB-C2 Standard is designed for use in the cable channel. The signal frame structure and preambles used in DVB-T2 may not be suitable to be reused in DVB-C2 Standard.
A frame header of Forward Error Correction (FEC) is designed for use in the DVB-C2 Standard. The FEC data block is composed of a Bose-Chaudhuri-Hocquenghem (BCH) outer code and a Low-Density-Parity-Check (LDPC) inner code. Two dimensional interleaving is also performed. Interleaving is a procedure for rearranging the order of a sequence to fulfill different objectives. For channels subject to selective fading over time and frequency domains, bit and/or symbol interleaving have been used in conjunction with channel coding to distribute the error bursts. A frame header is attached in front of each FEC frame to indicate the coding rate, modulation type and physical layer pipe identifier. Besides the signaling of physical layer related information, the FEC frame header has to provide a structure so that it can be easily and reliably detected in the receiver.